1. Field of the Invention
The present invention relates to highly active supported catalyst systems comprising metallocene(s) and cocatalyst(s) such as alumoxane(s), which can advantageously be used in olefin polymerization and to a process for the economical preparation of such catalyst systems, to a process using such catalyst systems for the polymerization and copolymerization of olefins and to polymers which are prepared using such catalyst systems.
2. Background of the Art
Metallocenes may be used as catalyst components for the polymerization and copolymerization of olefins, possibly in combination with one or more cocatalysts. In particular, halogen-containing metallocenes are used as catalyst precursors, which can be converted, for example, by an aluminoxane, to polymerization-active cationic metallocene complexes (EP 0 129 368, EP 0 284 708 or EP 0 302 424).
The synthesis of such metallocenes is well known (U.S. Pat. Nos. 4,752,597; 5,017,714; 5,391,790; 5,616,747 or EP Patent Nos. 0 320 762; 0 416 815; 0 537 686 and 0 669 340). They may be produced, for example, by reacting cyclopentadienyl metal compounds with halides of transition metals, such as titanium, zirconium, and hafnium.
It is also well known that basic properties of the metallocenes, such as polymerization activity, stereoselectivity, regioselectivity, and maximum achievable polymer molecular weight can be systematically controlled by specific substitution patterns of the ligand sphere. However, to use metallocenes for the stereoselective and regioselective polymerization of olefins, the preparation of the isomerically pure racemic form is absolutely necessary, since the corresponding meso form produces undesired atactic polymer, like atactic polypropylene. The isomerically pure racemic form is understood to mean a rac:meso ratio of at least 5, and preferably 10.
Such stereoselective and/or regioselective metallocenes for the polymerization of olefins to polyolefins especially for the polymerization of propylene or the copolymerization of propylene with other olefins and which are useful and preferred as metallocenes for the catalyst systems of the present invention, are well known in the literature. As an example, such metallocenes are disclosed in U.S. Pat. Nos. 4,530,914; 4,542,199; 4,769,910; 4,808,561; 4,871,705; 4,931,417; 4,933,403; 4,937,299; 5,017,714; 5,026,798; 5,057,475; 5,120,867; 5,132,381; 5,145,819; 5,155,180; 5,198,401; 5,239,022; 5,243,001; 5,276,208; 5,278,119; 5,296,434; 5,304,614; 5,324,800; 5,328,969; 5,329,033; 5,350,723; 5,374,752; 5,391,790; 5,416,178; 5,436,305; 5,455,366; 5,510,502; 5,532,396; 5,543,373; 5,554,704; 5,576,260; 5,612,428; 5,616,663; 5,629,254; 5,635,437; 5,661,096; 5,672,668; 5,679,812; 5,723,640; 5,739,366; 5,741,868; 5,770,753; 5,786,432; 5,830,821; 5,840,644; 5,840,948; 5,852,142; 5,929,264; 5,932,669; 6,017,841; 6,051,522; 6,051,727; 6,057,408; 6,087,291; 6,100,214; 6,114,479; 6,117,955; 6,124,230; 6,140,432; 6,194,341; 6,218,558; 6,228,795; 6,242,544; 6,245,706; 6,252,097; 6,255,506; 6,255,515; 6,376,407; 6,376,408; 6,376,409; 6,376,410; 6,376,411; 6,376,412; 6,376,413; 6,376,627; 6,380,120; 6,380,121; 6,380,122; 6,380,123; 6,380,124; 6,380,330; 6,380,331; 6,380,334; 6,399,723; 6,444,606; 6,469,114 and US Application Nos. 2001021755; 20030149199 and EP 576 970; EP 611 773, and WO 97/32906; WO 98/014585; WO 98/22486; WO 00/12565; WO 01/48034; WO 03/045964; WO 03/106470.
Processes for preparing polyolefins using soluble, homogeneous catalyst systems comprising a transition metal component of the metallocene type and a cocatalyst component of the type of an aluminoxane are well known. In polymerizations using such soluble, homogeneous catalyst systems, heavy deposits are formed on reactor walls and the stirrer if the polymer is obtained as a solid. These deposits are formed by agglomeration of the polymer particles whenever metallocene and/or cocatalyst are present in dissolved form in the suspension. The deposits in the reactor systems quickly reach considerable thickness and have a high strength. They prevent heat exchange to the cooling medium and therefore have to be removed regularly. Such homogeneous catalyst systems cannot be used industrially in liquid monomer or in the gas phase.
To avoid deposit formation in the reactor, supported catalyst systems in which the metallocene and/or the aluminum compound serving as cocatalyst is/are fixed on an inorganic support material have been proposed. As an example, in EP-A-0 576 970 or WO 01/48034 metallocenes and corresponding supported catalyst systems are disclosed. Such supported catalyst systems give polymers, in particular polypropylenes, having melting points of up to about 156° C.
A variety of different processes for preparing supported catalysts are known. As described in WO 94/28034 supported metallocene catalysts can, for example, be obtained by mixing a metallocene and aluminoxane containing solution with the support material and removing the solvent in vacuum. The solution volume of the impregnation solution is thereby greater than the pore volume of the support material.
In another process, the metallocene containing solution is mixed with the support material whereby the solution volume of the impregnation is equal or smaller than the pore volume of the support material (WO 94/14856). The solid catalyst can be isolated as a dry powder by removing the solvent under vacuum.
Other supported metallocene catalyst systems are disclosed in WO 98/01481. Here a metallocene is dissolved in a solvent and precipitated by addition of another solvent in which the metallocene compound is only slightly soluble in the presence of the support material. Thereby, the catalyst is immobilized on the surface and within the pores of the support.
Yet another supported metallocene catalyst can be obtained by impregnation of a support material with an impregnation solution comprising the metallocene component, wherein the impregnation solution flows through the support material (WO 00/05277).
In general, the main deficiency of such supported catalyst systems, developed up to now, is their low productivity under industrially relevant polymerization temperatures of from 50° C. to 100° C. As a consequence, the industrial usefulness of these catalysts is questionable as long as the commercial competitiveness against the established Ziegler-Natta titanium catalysts is not reached. As the necessary catalyst components like metallocenes and cocatalysts are in general expensive chemicals, improvements of the competitiveness by reducing the catalyst costs are limited and the only other option is to increase the catalyst productivity.
The object of the present invention is to address this main disadvantage of the state of the art catalyst systems and to provide supported catalyst systems with improved polymerization performance under industrially relevant polymerization conditions at temperatures of from 50° C. to 100° C.
Furthermore, it is an object of the present invention to provide an economical process for preparing supported metallocene catalysts, which is universally applicable e.g. with regard to different metallocene components and which results in catalyst systems with improved catalyst productivities. The resulting supported catalysts should be homogeneously loaded and should lead to good polymer particle morphologies.
Another object of the present invention is to provide supported metallocene catalysts obtained by the above described process and to provide an environmentally friendly and economical process for preparing polyolefins under industrially relevant polymerization conditions using the catalyst systems of this invention.